The invention relates to a manufacturing and assembly method and construction for a sound pickup needle for the scanning of mechanical sound carriers, preferably records.
A distinction is made in such needles between the so called unmounted and mounted needles. While the former consist of integral parts, preferably diamond, the latter only have a point consisting of the actual needle material whereas the rest of the needle is made of another material which, under circumstances, can be considerably softer. The needle point is then cemented or soldered to this material.
In the description of the invention which now follows, diamond is assumed to be the needle material for the sake of simplicity, although other suitable materials such as sapphire or ruby can also be processed by the same manufacturing process according to the invention.
Traditional, unmounted diamonds have the advantage, among others, of a small mass because the specific gravity of diamond is lower than that of the carrier materials usually used for mounted needles.
Disadvantages of unmounted diamonds are the requirement for a more complicated grinding operation and difficulties encountered therein in obtaining exactly ground shapes, a higher raw material price, and a relatively great mass.
As mentioned, mounted diamonds consist of a diamond point and a usually cylindrical shaft of steel or another suitable carrier material.
Used as a point in a diamond chip which is first soldered to the carrier and then ground to the desired shape in the subsequent grinding operation.
Such a mounted needle is easier to machine because handling the carrier is easier, and an optical inspection of the ground needle through light reflection to the usually light-impermeable carrier is also possible more easily than when transparent, unmounted diamonds are involved.
In both cases, the assembly of the needles into the needle carrier tube of the sound pickup, which transfers the needle motion when scanning the record to an element serving the transformation into electrical signals, is difficult. This carrier tube usually has a through hole into which the needle is inserted. After straightening of the needle, it is cemented in the carrier tube. When elliptical or similar ground shapes are involved, this straightening is most important, since scanning errors will result otherwise which, in extreme cases, can lead to damage to the records being played.